Combined handset and pots filter

ABSTRACT

The present invention is generally directed to a telephone handset for testing the transmission quality of a local loop. In accordance with one aspect of the invention, the telephone handset includes a connector configured to connect to the local loop at, for example, a junction box. The invention also includes a low-pass filter circuit electrically interposed between the connector and operational circuitry of the telephone handset. In operation, the low-pass filter is designed to pass (substantially undisturbed) electrical signals within the POTS frequency band from the connector to the operational circuitry. In the same way, the low-pass filter is designed to substantially block the passage of electrical signals above the POTS frequency range. In this way, the low-pass filter blocks the introduction of high frequency signals, which may otherwise generate intermodulation products within the audible range, from reaching the operational circuitry of the testing handset. In accordance with another feature of one embodiment of the invention, a device is provided for detecting the presence of xDSL signals on a local loop. In accordance with this embodiment, at least one band-pass or high-pass filter is added in parallel with the low-pass filter. The output of the at least one band-pass or high-pass filter is then analyzed to determine whether an xDSL signal is present within that frequency band (defined by the at least one band-pass or high-pass filter).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to telephone handsets,and more particularly to an improved telephone handset for use intesting lines carrying both POTS and xDSL communications.

[0003] 2. Discussion of the Related Art

[0004] In recent years telephone communication systems have expandedfrom traditional plain old telephone system (POTS) communications toinclude high-speed data communications as well. As is known, POTScommunications includes not only the transmission of voice information,but also PSTN (public switched telephone network) modem information,control signals, and other information that is transmitted in the POTSbandwidth, which extends from approximately DC to approximately 3.4kilohertz.

[0005] New, high-speed data communications provided over digitalsubscriber lines, such as Asymmetric Digital Subscriber Line (ADSL),Rate Adaptive Digital Subscriber Line (RADSL), etc. (more broadlydenoted as xDSL) provide for high speed data transmissions, as iscommonly used in communicating over the Internet. As is known, thebandwidth for xDSL transmissions is generally defined by a lower cutofffrequency of approximately 30 kilohertz, and a higher cutoff frequencywhich varies depending upon the particular technology. Since the POTSand xDSL signals are defined by isolated frequency bands, both signalsmay be transmitted over the same two-wire loop.

[0006] A POTS splitter is typically provided at each end of atransmission system communicating both POTS and xDSL information. As isknown, a POTS splitter circuit consists of a high-pass filter and alow-pass filter, which are used to separate the two signals (the POTSsignal from the xDSL signal). Normally, the high-pass filter is builtinto the xDSL transceiver, whereas the low-pass filter (commonlyreferred to as a POTS filter) normally provided as a separate unit. Inoperation, the POTS filter operates to filter the high frequency xDSLsignals in order to protect the POTS (e.g., telephone) circuitry. At thesame time the POTS filter provides filtering and protection for higherfrequency noise signals that are often associated with a ring signal, orthe switching circuitry of a central office.

[0007] It has been found, however, that troubleshooting line problems onlocal loops carrying both POTS and xDSL communications is frequentlymore difficult than troubleshooting a POTS only local loop. Years ago,the service provider (phone company) installed telephone lines from thecentral office, all the way to the telephone. Thus, the service providerwas responsible for the integrity of the line all the way to thetermination point (at the telephone). However, in recent years, it hasbecome the custom for the service provider to run the local loop only toa junction box at the customer premises (whether the customer premisesis a business, personal residence, etc.). Therefore, when performingtesting on the local loop, the service provider is responsible only forinsuring the integrity of the local loop between the central office andthe junction box at the customer premises.

[0008] Typically, testing of a line is performed by a service technicianusing a testing handset to test the line. Alternatively, testing may beperformed using more elaborate and specialized test equipment such as atransmission impairment measurement system (TIMS). The technician willplug the testing handset into a junction of the line to test the qualityof the communications at that junction, and thus verifying the integrityof the line between the junction and the central office. Usually, thejunction tested is the junction provided at the customer premises. Inshort, this form of testing is performed “by ear”, wherein the fieldtechnician evaluates the line quality by listening to the quality of thesound/signal at the testing handset.

[0009] It has been found that a problem in this manner of testing oftenarises when there are shared communications on the same local loop. Forexample, when the customer not only has POTS service, but alsosubscribes to an xDSL service, technicians testing the line qualityoften detect noise signals within the POTS frequency band, when testingthe line at the junction box, which noise signals are not audiblypresent on POTS telephones inside the customer premises.

[0010] Accordingly, it is desired to provide an improved method orapparatus for testing local loops that overcomes the shortcomings anddisadvantages noted above.

SUMMARY OF THE INVENTION

[0011] In researching the shortcomings of the manner of testing linequality and in the testing handsets used in the prior art, it wasdetermined that many of the perceived line problems were actually theresult of intermodulation products. Testing handsets, as with othercommon telephone handsets, include internal circuitry that generatesintermodulation products when receiving high frequency signals; theintermodulation product being a signal having a frequency defined by thedifferential of two higher frequency, received signals. When xDSLcommunications are occurring at the same time the technician is testingthe line, intermodulation products generated by the handset from thehigh-frequency xDSL transmissions often generate noise in the audiblefrequency band, which interferes with the proper evaluation of the linetest conducted by the technician. Since POTS filters are disposedbetween the junction box and the POTS telephones at the customerpremises (for those customer premises having a xDSL communicationservice), such intermodulation noise signals are not present at the POTStelephones.

[0012] When a field technician is dispatched to test a local loop at acustomer premises, the technician does not necessarily know whether thatcustomer premise includes a xDSL service. Even if the service technicianis made aware that the customer premises includes an xDSL service, thetechnician will still not know whether a device within the customerpremise is transmitting information within the xDSL frequency band atany given time.

[0013] Certain objects, advantages and novel features of the inventionwill be set forth in part in the description that follows and in partwill become apparent to those skilled in the art upon examination of thefollowing or may be learned with the practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outin the appended claims.

[0014] To achieve the advantages and novel features, the presentinvention is generally directed to a telephone handset for testing thetransmission quality of a local loop. In accordance with one aspect ofthe invention, the telephone handset includes a connector configured toconnect to the local loop at, for example, a junction box. The inventionalso includes a low-pass filter circuit electrically interposed betweenthe connector and operational circuitry of the telephone handset. Inoperation, the low-pass filter is designed to pass (substantiallyundisturbed) electrical signals within the POTS frequency band from theconnector to the operational circuitry. In the same way, the low-passfilter is designed to substantially block the passage of electricalsignals above the POTS frequency range. In this way, the low-pass filterblocks the introduction of high frequency signals, which may otherwisegenerate intermodulation products within the audible range, fromreaching the operational circuitry of the testing handset.

[0015] In accordance with the preferred embodiment of the presentinvention, the low-pass filter circuit is defined by a cutoff frequencyranging from approximately 3.4 kilohertz to approximately 10 kilohertz.In addition, means are further included for bypassing the low-passfilter. Preferably, this “bypass” means includes a manually-operatedswitch, such as a double-pole, double throw switch. Such a switch allowsthe service technician to switch the low-pass filter into and out of thecircuitry, when desired. Alternatively, the “bypass” means may beautomatically implemented. In this regard, circuitry may be provided tosense the presence of high frequency signals (i.e., signals in the xDSLfrequency band) that may otherwise generate unwanted intermodulationnoise in the audible frequency. Upon sensing such signals, the “bypass”means may be configured to automatically switch in the low-pass filtercircuitry.

[0016] In will be appreciated that, consistent with the concepts andteachings of the present invention, the low-pass filter may be either anactive filter or passive filter. Furthermore, depending upon theintended operating environment, the low-pass filter may be designed tohave varying input impedance. For example, in a first operatingenvironment, it may be desirable to design the low-pass filter with ininput impedance of approximately 600 ohms, while in another embodiment,it may be desired to design the filter to have an input impedance ofapproximately 900 ohms.

[0017] In accordance with another aspect of the invention, an improvedtelephone handset for normal POTS communication may be provided. In thisregard, the inventive aspects and features summarized above may beincorporated into a typical POTS telephone, along with a mechanism forautomatically detecting the presence or transmission of an xDSL signalon the line. In response to such detection, the mechanism is operativeto switch in the low-pass POTS filter. In this way, the low-pass filteris utilized only when needed. Such a telephone may be utilized at acustomer premises having a xDSL service and a xDSL communication device,and thus eliminate the need for separately install a POTS filter at thecustomer premises. In this regard, a handset including the “bypass”means feature described above may be mass produced at a reasonably lowcost and provided to subscribers of xDSL services, particularly wherethat service will share a common local loop with POTS communicationdevices.

[0018] In accordance with yet another aspect of an embodiment of theinvention, a device is provided for detecting the presence of an xDSLsignal on a local loop. In accordance with this aspect, the deviceincludes an input electrically connected to the local loop and a firstfilter electrically connected to the input for passing signals within aPOTS frequency band. A second filter is electrically connected to theinput for passing signals having frequency components above the POTSfrequency band. Preferably, the second filter will be defined by a highinput impedance, so that POTS signals passing through the first filterare substantially undisturbed. A signal detector is electricallyconnected to an output of the second filter for detecting the presenceof a signal having a frequency above the POTS frequency band, and asignaling means is provided for signaling that a signal having afrequency above the POTS frequency band has been detected.

DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings incorporated in and forming a part ofthe specification, illustrate several aspects of the present invention,and together with the description serve to explain the principles of theinvention. In the drawings:

[0020]FIG. 1 is graph showing the power spectrum for POTS and xDSLtransmission bands;

[0021]FIG. 2 is a block diagram illustrating the principal components ofa prior art telecommunication system, at both the central office andcustomer premises;

[0022] FIGS. 3A-3C are block diagrams illustrating alternativeembodiments of the present invention;

[0023] FIGS. 4A-4C are schematic diagrams illustrating alternativefilter structures for implementing the low-pass filter of the presentinvention;

[0024] FIGS. 5A-5B are schematic diagram illustrating alternative filtercircuits for realizing different input impedance values; and

[0025]FIGS. 6A and 6B are block diagrams illustrating another feature ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026] Having summarized various aspects of the present invention,reference will now be made in detail to the description of the inventionas illustrated in the drawings. While the invention will be described inconnection with these drawings, there is no intent to limit it to theembodiment or embodiments disclosed therein. On the contrary, the intentis to cover all alternatives, modifications and equivalents includedwithin the spirit and scope of the invention as defined by the appendedclaims.

[0027] Turning now to the drawings, FIG. 1 is a diagram illustratingfrequency band communications, as is known in the prior art. The termfrequency band communications is used to indicate communication ofinformation within a certain defined, frequency band. As is known in theprior art, plain old telephone system (POTS) communications aretransmitted in the frequency band 12 defined between about 0 (DC) andabout 4 kHz. A second transmission frequency band 14 is defined at ahigher frequency level than the POTS frequency band 12, and is used inthe transmission of digital subscriber line (DSL) communications. Aguard dead band 16 is typically provided to separate the twotransmission frequency bands 12 and 14. The DSL transmission frequencyband 14 is more broadly denominated as “xDSL”, wherein the “x”generically denominates any of a number of transmission techniqueswithin the DSL family. For example, ADSL—asynchronous digital subscriberline, RADSL—Rate Adaptive Digital Subscriber Line, HDSL—high-bit-rateDSL, etc. As is known, xDSL transmission frequency bands 14 mayencompass a bandwidth of greater than 1 MHz, but the specific uppercutoff frequency will vary depending upon that particular xDSL service.As a result, without the addition of extra equipment such as POTSfilters, splitters, etc. xDSL signals are not compatible with attachedPOTS type equipment, such as telephones, PSTN modems, facsimilemachines, etc.

[0028] Referring now to FIG. 2, a prior art communication system isshown. Specifically, FIG. 2 illustrates communication between a centraloffice 20 and a customer premises 22 by way of local loop 24. AlthoughFIG. 2 illustrates a central office 20, it will be appreciated that asimilar illustration may be used to depict communication between acustomer premises 22 and a remote terminal, other than a central office,having substantially the same functionality illustrated in connectionwith the central office 20. Therefore, FIG. 2 is not intended to limitedthe environment of the present invention, as described herein.

[0029] While the customer premises 22 may be a single dwellingresidence, a small business, or other entity, it is generallycharacterized as having POTS equipment, such as a telephone 26, PSTNmodem 27, fax machine (not shown), etc. The customer premise 22 may alsoinclude an xDSL communication device, such as an xDSL modem 28. When anxDSL service is provided, a POTS filter 30 is interposed between thePOTS equipment 26 and the local loop 24. As is known, the POTS filter 30includes a low-pass filter having a cut-off frequency of approximately 4kilohertz to 10 kilohertz, in order to filter high frequencytransmissions from the xDSL communication device 28 and protect the POTSequipment.

[0030] At the central office 20, additional circuitry is provided.Generally, a line card containing line interface circuitry is providedfor electrical connection to the local loop 24. An xDSL modem, includingboth receiver and transmitter circuitry, is broadly denoted by block 42.This circuitry is directly connected for communications across the localloop 24. The remaining POTS circuitry is separated, or buffered, fromthe local loop 24 by POTS filter 44. Specifically, other circuitrycommonly carried on the line interface card includes a hybrid 46,off-hook detection circuitry 48, and ring generator circuitry 50.Typically, the hybrid circuitry is intermittently connected to the localloop 24 by a switching means (not shown). As is known, a hybrid circuit46 is a device for translating between two-wire and four-wirecommunication links. For purposes of illustration, it is important tonote that voice and other POTS information is communicated through theblock denoted as hybrid circuitry 46 to/from the local loop 24. As iswell known, the off-hook detection circuitry 48 is the circuitryutilized at the central office to detect when a user at the customerpremises 22 has lifted a telephone handset or otherwise has sought toestablish communications from a POTS device.

[0031] The ring generation circuitry 50, in a manner that is known,generates a ring signal for communication across the local loop 24, tocause a telephone 26 or other POTS equipment to ring at a customerpremises 22. Typically, the ring generation circuitry 50 is disconnectedfrom the local loop 24 by way of a normally open switching means (notshown). To minimize the deleterious effects of various noise signals andto protect the various POTS circuitry, the POTS filter 44 provideslow-pass filtering having a cutoff frequency above the approximately 3.4kilohertz upper frequency band edge.

[0032] As is known, and briefly discussed above, there are a variety ofreasons in which a person located at a customer premises 22 mayexperience line problems that manifest themselves as noise on thereceiver of a telephone handset 26. The customer may then report theproblem to the central office (phone company), which dispatches a fieldservice technician to troubleshoot and isolate the problem. In thisregard, the field service technician typically utilizes a test phone 60,known to be in good working order, and may check the local loop 24 byconnecting the test phone 60 to any of a number of junction boxes 62,64, and 66. These junctions may be located at or near the central office20 (e.g., junction 66), at or near the customer premises 22 (e.g.,junction 62), or at intermediate locations (e.g., junction 64). Thefield service technician connects the test phone 60 to the local loop 24at the test junction 62, 64, 66, then listens to the handset todetermine any “perceived” noise or poor signal quality on the line.Although the illustrated embodiment is described herein in connectionwith a test phone 60, it will be appreciated that the concepts andteachings of the present invention apply equally to other types oftesting devices, such as a TIMS. Accordingly, the invention andinventive concepts are not to be unduly limited to the test phoneembodiment discussed herein.

[0033] A problem, however, is encountered when higher frequencytransmissions, such as xDSL data transmissions, are being communicatedacross the local loop 24. Since the field service technician is oftenunaware that the customer may have an xDSL service or, even if he or sheknows that the customer premises is equipped with an xDSL service,whether xDSL transmissions are current underway, a field servicetechnician does not know whether/when to discount certain noise signals.

[0034] As described previously, such higher frequency xDSL transmissionsinteract with operational circuitry of the test phone 60 to generateintermodulation products in the form of lower frequency noise signals,often within the POTS (i.e., audible) frequency band. In fact, since thecustomer premises 22 is typically configured with a POTS filter 30, thenoise observed by the field service technician is usually not present onthe customer premises telephone 26, therefore making problemverification and isolation even more difficult for the field servicetechnician.

[0035] In order to avoid this and other shortcomings of the prior art,the preferred embodiment of the present invention is directed to animproved telephone test handset for use by field service technicians introubleshooting reported line problems of a local loop 24. Referring toFIG. 3A, a first embodiment of the present invention is illustrated. Inthis embodiment, the test telephone 60 used by a field servicetechnician includes an input lead terminated at a connector 68, whichconnector may be plugged directly into a jack provided at a junctionbox. For example, the connector 68 may be in a form of a standard RJ-11plug. As is known, the telephone 60 includes operational circuitry 70which provides for the functional aspects of the telephone. Since thevarious operational circuitry and functional aspects of varioustelephones are known in the art, the structure and operation of theoperational circuitry 70 need not be described herein. Instead,reference is more particularly directed to the low-pass filter 72, whichis the primary component of the present invention.

[0036] As is illustrated, the low-pass filter 72 is electricallyinterposed between the connector 68 and operational circuitry 70 foroperation integrally therewith. Preferably, the low-pass filter 72 isdesigned to pass signals having frequency components in the POTSbandwidth, or approximately DC to approximately 3.4 kilohertz. In thepreferred embodiment, the low-pass filter 72 may be designed to have anupper cutoff frequency in the range of 4 kilohertz to 10 kilohertz.Providing a slightly higher cutoff frequency may be desired foroperation of the present invention in many foreign countries, since manycountries are known to provide control signaling in the frequency bandjust above the POTS frequency band. Thus, by extending the upper cutofffrequency into a slightly higher frequency range, the telephone handset60 constructed in accordance with the present invention is readilyadapted for use in a variety of foreign countries, as well as the UnitedStates.

[0037] Referring briefly to FIGS. 4A through 4C, several alternativelow-pass filter circuit designs are shown. Specifically FIG. 4A shows asimple second order LC filter, while FIGS. 4B and 4C illustrate thirdand fourth order LC filters, respectively. It will be appreciated thatthe filter designs illustrated in FIGS. 4A through 4C are providedmerely for purposes of illustration, and are not deemed to be alimitation on the present invention. Indeed, the present invention isdirected to the broader aspect of combining a low-pass, POTS filter inconnection with a telephone handset, which has not heretofore been done.The specific design and implementation of the filter may vary dependingupon a number of factors, including intended operational environment.

[0038] Indeed, the filter embodiments illustrated in FIGS. 4A through 4Cillustrate simple LC filters. In practice, it may be desired to providean active, as opposed to passive, filter to achieve the performancecharacteristics associated therewith. In this regard, the power sourcerequired to source the various components in an active filter (e.g.,operational amplifiers) may be provided by a separate battery sourcewithin the telephone handset, or may be obtained from the powercommunicated across the local loop 24.

[0039] To further illustrate various differing filtering embodiments,reference is hereby made to FIGS. 5A and 5B. In this regard, FIG. 5Aillustrates a particular filter having an input port 86 and an outputport 87. In FIG. 5A, the various filter component values (e.g., chokevalues and capacitor values). FIG. 5A illustrates a balanced filterhaving four chokes L1, L2, L3, and L4, wherein chokes L1 and L2 havecomponent values of six milli-henries, while chokes L3 and L4 each havecomponent values of nine milli-henries. Similarly, the filter of FIG. 5Ahas capacitors C1 and C2 having component values of 0.047 micro-faradsand 0.027 micro-farads, respectively.

[0040] Significant with respect to the illustrated embodiment, thefilter of FIG. 5A not only realizes a low-pass filter having an uppercutoff frequency in the desired 4 kilohertz to 10 kilohertz frequencyrange, but it also provides an input impedance (as seen at port 86) ofapproximately 600 ohms. Such filter characteristics, namely the inputimpedance, is preferred when the testing performed by the field servicetechnician is performed at the customer premises (e.g., junction 62 ofFIG. 2). When, however, the testing is performed at the central office(e.g., junction 66 of FIG. 2) a 900 ohms input impedance may bepreferred. In this regard, reference is made briefly to FIG. 5Billustrating yet another embodiment of a filter circuit constructed inaccordance with the preferred embodiment. Like the filter circuit ofFIG. 5A, the circuit of FIG. 5B has in input port 88 and an output port89. Using the component values provided in the drawing, it may bereadily verified that the input impedance as seen at port 88 of thecircuit of FIG. 5B is approximately 900 ohms. Thus, the circuit of FIG.5B may be preferred when testing is performed at or near the centraloffice 20.

[0041] Returning now to FIG. 3, and referring specifically to FIGS. 3Band 3C, alternative embodiments of the present invention are shown.Referring first to FIG. 3B, it may be desired to provide a testtelephone 160 that employs switching means, which allow the fieldservice technician to either activate or deactivate the low-pass filtercircuit of the telephone 160. In this regard, a simple double-poledouble-throw manually-operated switch 74, 76 may be provided. When thewiper arms of the double-pole switch 74, 76 are disposed in a firstconfiguration, the low-pass filter circuit 72 is switched into thecircuit, so as to be electrically interposed between the connector 68and the operational circuitry 70. When, however, the wiper arms of thedouble-pole switch 74, 76 are motivated to a second position, a shortcircuit 73 may be established to bypass the low-pass filter circuit 72,so that the connector 68 is directly connected to the operationalcircuitry 70.

[0042] Taking this concept one step further, consistent with theconcepts in teachings of the present invention, the telephone handset260 illustrated in FIG. 3C may be provided. The circuitry of thisembodiment is similar to that of FIG. 3B, except that the circuitry ofthe telephone handset 260 may include a plurality of differing low-passfilter circuits 72, 80. As was discussed in connection with FIGS. 5A and5B, it may be desired, depending upon where the test point is located,to employ testing telephones having low-pass filter circuits ofdiffering characteristics (namely input impedance, cutoff frequencies,roll off rate, or other characteristics). In this regard, such differinglow-pass filter circuits may be employed in a single telephone handset260, and individually connectable by way of switching means to beselectively interposed between the connector 68 and the operationalcircuitry 70. In this regard, a manually-operated double-pole rotaryswitch 78, 79 may be provided to electrically connect filter circuits1-n 72-80, between the connector 68 and operational circuitry 70.Similarly, as described in connection with FIG. 3B, a separate shortcircuit line 73 may also be provided, to effectively remove any low-passfiltering from the circuit interconnecting connector 68 and operationalcircuitry 70. In this way, a single test phone 260 may provide a rotaryswitch, for example, to allow a field service technician to select alow-pass filter having characteristics uniquely tailored to theenvironment or testing location at hand.

[0043] Referring now to FIG. 6A, another feature of the presentinvention is shown. Specifically, a line testing device constructed inaccordance with the present invention may be constructed to detect thepresence of an xDSL signal. Upon detection, the low-pass (or POTS)filter may be switched into the circuit. This detection feature may beprovided independently, or may be provided in connection with circuitryoperable to automatically switch in or out the POTS filter upondetection of an xDSL signal.

[0044] In the manner describe above in connection with FIG. 3B, alow-pass (or POTS) filter 172 may be provided, along with a bypassconnection 173. When no xDSL communications are taking place, theswitching means 174, 176 may be switched (either manually orautomatically) to bypass the low-pass filter 172. Otherwise, when xDSLcommunications are occurring, then the switching means 174, 176 may becontrolled to switch the low-pass filter 172 into the operativecircuitry.

[0045] The detection circuitry may be provided by a high-pass filter 104and energy detection circuitry. In this regard, the high-pass filter isdesigned to have a lower cutoff frequency that is higher than the upperfrequency POTS band, thereby passing only xDSL signals. The energydetection circuitry 106 is designed to generate an output signalwhenever an energy level (higher than a predetermined value) isdetected. It will be appreciated that the high-pass filter willpreferably be designed with a high input impedance, so as to haveminimal impact or affect upon the line. The output of the energydetection circuitry may be directed to an LED 108 or other signalingmechanism to provide an indication (either visual or audible) that xDSLcommunications are occurring. This will serve as an indication to thefield service technician that the low-pass filter 172 should be switchedinto the circuitry. The output of the energy detection circuitry mayalso be used as the control mechanism for the switching means 174, 176.

[0046] A further embodiment of the present invention is illustrated inFIG. 6B. This embodiment is similar to that of FIG. 6A, except that itincludes multiple band-pass filters BP #1, BP #2, and BP #n. Energydetection circuitry is provided in connection with the output of each ofthe band-pass filters. This embodiment of the present inventionrecognizes that each of the various xDSL communication services has aslightly different frequency signature, and such services can bedetected individually by evaluating the energy profile at differentfrequencies. It will be appreciated that the embodiment of FIG. 6B maynot only be used in isolation to detect and identify different xDSLcommunications, but may also be used in connection with an embodimentsuch as that illustrated in FIG. 3C. Specifically, based upon thespecific xDSL service detected, it may be desired to switch in adifferent low-pass filter (either manually or automatically).

[0047] It will be appreciated that FIG. 6B has been presented merely forpurposes of illustrating the broader concepts of a feature of analternative embodiment of the invention. The broader functionality ofthis feature may be implemented in a variety of different ways. Forexample, the functionality of FIG. 6B may be achieved by an embodimentsimilar to FIG. 6A, but with the addition of an analog to digitalconverter disposed at the output of the high-pass filter. The output ofthe analog to digital converter may be processed by a processor, such asa microprocessor or digital signal processor, to analyze the frequencycomponents of the signal, and thus ascertain the frequency signaturethereof. This may be implemented, for example, by computing the FourierTransform (e.g., computing the fast fourier transform or FFT) of thesignal output from the analog to digital converter. The FourierTransform can then be processed to evaluate the frequency components ofthe signal. Of course other methods of evaluating the frequencysignature of the signal may be implemented in place of the FFT.

[0048] The xDSL detection and identification capability discussed abovemay be desired for a variety of reasons. For example, a central officemay wish to police its lines to ensure that no xDSL services areprovided. Suppose, for example, that a central office has leased anumber of local loops to another service provider (e.g., long-distancetelephone service provider), under the express contractual limitationthat xDSL services are not permitted. To police such a lease agreement,the central office may connect a handset with the xDSL identificationfeature into a MDF (main distribution frame) at the central office.Similarly, certain local loops extending from a central office may bepermitted to accommodate certain xDSL services, but limited to onlycertain predefined xDSL services. Accordingly, the above-describedidentification feature may be used to ensure that no impermissible xDSLservices are being used.

[0049] While the various objects, advantages, and features of thepresent invention have been described herein in connection with a testphone of the type used by a field service technician, it will beappreciated that certain aspects of the present invention may also beincorporated into a telephone of the type (e.g., 26) used in a customerpremises 22. As is illustrated in connection with FIG. 2, when acustomer premises 22 is equipped with an xDSL service, a POTS filter maybe installed to protect the various POTS equipment from the highfrequency transmissions at the xDSL modem 28. Preferably, the POTSfilter will be selectivly switched in and out of the circuitry asneeded, base upon the presence of xDSL signals on the line.Particularly, in environments where telephones 26 are the only POTSequipment at the customer premises, using a telephone constructed inaccordance with the present invention, would accordingly eliminate theneed for a separately installed POTS filter 30 at the customer premises.

[0050] The foregoing description has been presented for purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Obviousmodifications or variations are possible in light of the aboveteachings. The embodiment or embodiments discussed were chosen anddescribed to provide the best illustration of the principles of theinvention and its practical application to thereby enable one ofordinary skill in the art to utilize the invention in variousembodiments and with various modifications as are suited to theparticular use contemplated. All such modifications and variations arewithin the scope of the invention as determined by the appended claimswhen interpreted in accordance with the breadth to which they are fairlyand legally entitled.

What is claimed is:
 1. A device for testing the transmission quality ofa local loop comprising: a connector configured to connect to the localloop; a low-pass filter circuit electrically connected to the connectorand interposed between the connector and operational circuitry of thedevice, the low-pass filter being designed to pass substantiallyundisturbed electrical signals within the POTS frequency band from theconnector to the operational circuitry, the low-pass filter beingdesigned to substantially block the passage of electrical signals abovethe POTS frequency range.
 2. The device as defined in claim 1 , whereinthe device is a testing handset.
 3. The device as defined in claim 1 ,wherein the device is a transmission impairment measurement system. 4.The device as defined in claim 1 , wherein low-pass filter circuit isdefined by a cutoff frequency ranging from approximately 3.4 kilohertzto approximately 10 kilohertz.
 5. The device as defined in claim 1 ,further including means for bypassing the low-pass filter.
 6. The deviceas defined in claim 5 , wherein the means for bypassing includes amanually-operated switch means.
 7. The device as defined in claim 6 ,wherein the manually-operated switch means includes a double-poledouble-throw switch.
 8. The device as defined in claim 5 , wherein themean for bypassing includes an automatically-operated switch means,responsive to means for sensing a high frequency signal component,wherein the high frequency signal component is in an xDSL frequencyband.
 9. The device as defined in claim 1 , wherein the low-pass filteris designed to have an input impedance of approximately 600 ohms. 10.The device as defined in claim 1 , wherein the low-pass filter isdesigned to have an input impedance of approximately 900 ohms.
 11. Thedevice as defined in claim 1 , wherein the low-pass filter is a passivefilter.
 12. The device as defined in claim 11 , wherein the low-passfilter is designed exclusively from inductors and capacitors.
 13. Thedevice as defined in claim 1 , wherein the low-pass filter is an activefilter.
 14. A device for testing a phone line, the improvementcomprising: a low-pass filter circuit electrically interposed between ahandset connector and operational circuitry of the handset, the low-passfilter designed to pass substantially undisturbed electrical signalswithin the POTS frequency band from the connector to the operationalcircuitry, the low-pass filter being designed to substantially block thepassage of electrical signals above the POTS frequency range.
 15. Animproved telephone for use in a system carrying both POTS and xDSLsignal transmissions, comprising: operational circuitry designed toprovide and support operational functions of the telephone; aninput/output connector for communicating signals in a POTS frequencyband between a local loop and the operational circuitry; a low-passfilter circuit; means for detecting the presence of an xDSL signal; andswitching means, responsive to the means for detecting, for selectivelyinterposing the low-pass filter circuit between the input/outputconnector and the operational circuitry of the telephone handset,whereby the switching means switches in the low-pass filter when an xDSLsignal is present.
 16. The telephone as defined in claim 15 , whereinlow-pass filter circuit is defined by a cutoff frequency ranging fromapproximately 3.4 kilohertz to approximately 10 kilohertz.
 17. Thetelephone as defined in claim 15 , wherein the switching means includesa manually-operated switch means.
 18. The telephone as defined in claim17 , wherein the manually-operated switch means includes a double-poledouble-throw switch.
 19. The telephone as defined in claim 15 , whereinthe switching mean includes an automatically-operated switch means,responsive to means for sensing a high frequency signal component,wherein the high frequency signal component is in an xDSL frequencyband.
 20. The telephone as defined in claim 15 , wherein the low-passfilter is designed to have an input impedance of approximately 600 ohms.21. The telephone as defined in claim 15 , wherein the low-pass filteris designed to have an input impedance of approximately 900 ohms. 22.The telephone as defined in claim 15 , wherein the low-pass filter is apassive filter.
 23. The telephone as defined in claim 22 , wherein thelow-pass filter is designed exclusively from inductors and capacitors.24. The telephone as defined in claim 15 , wherein the low-pass filteris an active filter.
 25. An improved telephone for use in a systemcarrying both POTS and xDSL signal transmissions, comprising:operational circuitry designed to provide and support operationalfunctions of the telephone; an input/output connector for communicatingsignals in a POTS frequency band between a local loop and theoperational circuitry; a plurality of low-pass filter circuits disposedfor selective interconnection between the input/output connector and theoperational circuitry; and switching means electrically connected to theinput/output connector, each of the plurality of low-pass filtercircuits, and the operational circuitry, the switching means adapted toselectively interconnect one of the plurality of low-pass filtercircuits between the input/output connector and the operationalcircuitry.
 26. The telephone as defined in claim 25 , wherein theswitching means includes a double-pole double-throw switch.
 27. Thetelephone as defined in claim 25 , wherein the switching means includesa multi-position double-pole rotary switch.
 28. A device for detectingthe presence of an xDSL signal on a local loop comprising: an inputelectrically connected to the local loop; a first filter electricallyconnected to the input for passing signals within a POTS frequency band;a second filter electrically connected to the input for passing signalshaving frequency components above the POTS frequency band, the secondfilter defined by a high input impedance so that POTS signals passingthrough the first filter are substantially undisturbed; a signaldetector electrically connected to an output of the second filter fordetecting the presence of a signal having a frequency above the POTSfrequency band; and signaling means responsive to the signal detectorfor signaling that a signal having a frequency above the POTS frequencyband has been detected.
 29. The device as defined in claim 28 , whereinthe second filter is a high-pass filter.
 30. The device as defined inclaim 28 , wherein the second filter is a band-pass filter.
 31. Thedevice as defined in claim 28 , further including a plurality of secondfilters, each defining differing frequency bands.
 32. The device asdefined in claim 28 , wherein the signal detector is a circuit definedto detect the presence of a predetermined amount of energy within afrequency band, the predetermined amount of energy indicative of thepresence of a signal within that frequency band.
 33. The device asdefined in claim 28 , wherein the signal detector includes a circuit forcomputing a Fourier Transform of the signal output from the secondfilter.
 34. The device as defined in claim 28 , wherein the signalingmeans produces a visual indicator.
 35. The device as defined in claim 34, wherein the signaling means includes at least one LED.
 36. The deviceas defined in claim 28 , wherein the signaling means produces an audibleoutput.